In crop production, there is a steady demand for stable production of high-quality plants and reduction of pesticide dependency. To that end, researchers are actively improving, breeding, and developing cultivars of plants resistant to pests and pathogenic microbes through useful plant biotechnologies, such as plant cell fusion and recombinant DNA techniques. Transgenic plants resistant to herbicides (Patent Document 1), viruses (Patent Document 2), and pests (Patent Document 3) have already been produced using recombinant DNA techniques. Furthermore, as listed below, several types of transgenic plants resistant to plant pathogenic microbes have been produced: transgenic plants showing resistance to pathogenic filamentous fungus, produced by introducing a gene of an enzyme which inactivates a toxin produced by the pathogenic fungus (Non-Patent Document 1); transgenic plants showing resistance to at least one pathogenic bacterium, produced by introducing a gene of an antibacterial protein derived from an insect (Patent Document 4); transgenic plants resistant to complex disease, produced by introducing a Japanese mustard spinach-derived gene (Patent Document 5); transgenic plants resistant to multiple diseases produced using the thionine gene (Patent Document 6); and transgenic plants resistant to complex disease produced using an acidic thaumatin-like protein gene (Patent Document 7). However, it is generally accepted that disease resistance achieved by introducing a single resistance gene is not sufficiently effective. Furthermore, some of the introduced genes have harmful effects on the growth, fertility, and such of the transformants, thereby hindering their practical application.
WRKY transcription factors have been reported to be involved in disease resistance of dicots such as Arabidopsis (Non-Patent Documents 2 to 6). Several OsWRKY genes of rice plants that confer disease resistance have been reported in recent years (Non-Patent Documents 7 to 14), but identification of genes with stronger disease resistance effects has been desired.
So far, the present inventors have isolated the OsWRKY45 gene that, upon overexpression, imparts to rice plants complex disease resistance (for example, resistance against rice blast caused by filamentous fungi or bacterial leaf blight caused by bacteria), and have succeeded in producing recombinant rice plants which overexpress OsWRKY45 using a maize ubiquitin promoter (Pmaize Ubi) (Patent Document 8 and Non-Patent Document 15). However, when OsWRKY45 was overexpressed using the maize ubiquitin promoter, although strong resistance (complex resistance) against complex diseases was imparted to recombinant rice plants, phenomena such as growth retardation was found to occur depending on the cultivation conditions (Non-Patent Document 15).
Prior art documents relating to the present invention are shown below:    [Patent Document 1] Japanese Patent Application Kokai. Publication No. (JP-A) H02-186925 (unexamined, published Japanese patent application)    [Patent Document 2] JP-A (Kokai) H04-330233    [Patent Document 3] JP-A (Kokai) H03-247220    [Patent Document 4] JP-A (Kokai) H07-250685    [Patent Document 5] JP-A (Kokai) 2004-329215    [Patent Document 6] JP-A (Kokai) 2003-88379    [Patent Document 7] JP-A (Kokai) 2003-199448    [Patent Document 8] WO 2006/126671    [Non-Patent Document 1] Windhovel, U. et al., Plant Physiol., 104, 119-125 (1994)    [Non-Patent Document 2] Kalde, M. et al., Mol. Plant Microbe Interact., 16, 295-305 (2003)    [Non-Patent Document 3] Li, J. et al., Plant Cell, 16, 319-331 (2004)    [Non-Patent Document 4] Robatzek, S. et al., Genes Dev., 16, 1139-1149 (2002)    [Non-Patent Document 5] Yu, D. et al., Plant Cell, 13, 1527-1540 (2001)    [Non-Patent Document 6] Chen, C. et al., Plant Physiol., 129, 706-716 (2002)    [Non-Patent Document 7] Xie, Z. et al., Plant Physiol., 137, 176-189 (2005)    [Non-Patent Document 8] Qiu, Y. et al., Chinese Science Bulletin, 49(20), 2159-2168 (2004)    [Non-Patent Document 9] Qiu, D. et al., Mol Plant Microbe Interact, 20(5), 492-499 (2007)    [Non-Patent Document 10] Liu, X. et al., J Plant Physiol, 164(8), 969-979 (2007)    [Non-Patent Document 11] Chujo, T. et al., Biochimica et Biophysica Acta (BBA)—Gene Structure and Expression, 1769(7-8), 497-505 (2007)    [Non-Patent Document 12] Chujo, T. et al., Biosci Biotechnol Biochem, 72(1), 240-245 (2008)    [Non-Patent Document 13] Tao, Z. et al., Plant Phys., 151, 936-948 (2009)    [Non-Patent Document 14] Qiu, Y. and D. Yu, Environmental and Experimental Botany, 65(1), 35-47 (2009)    [Non-Patent Document 15] Shimono, M. et al., Plant Cell, 19, 2064-2076 (2007)